The present invention is directed to a process for dyeing fibrous substrates which comprises the steps of: providing a fibrous substrate; providing at least one sulfur dye; providing at least one reduction stable direct dye; and applying said reduction stable direct dye to said fibrous substrate in the presence of a suitable reducing agent.
As has been known for many years, sulfur dyes are advantageously used in the dyeing and/or printing of cellulose fiber materials and/or cellulosic blended textile fibers. In traditional dyeing processes the sulfur dyes are applied in the alkali soluble (pre)reduced form, i.e. xe2x80x9cleuco statexe2x80x9d, and are brought in contact with the cellulosic fibers in one of a variety of methods and subsequently oxidized in order to achieve color development and/or impart a degree of dye fastness to the dyed cellulosic textile substrate.
Reducing agents traditionally employed for the application of sulfur dyes are in particular: sodium hydrogen sulphide, sodium sulfide and sodium polysulphides. Other chemical reducing agents that do not contain sulfide ions (i.e. xe2x80x9cnon-sulfidexe2x80x9d reducing agents) known to be useful for the reduction of sulfur dyestuffs include: sodium borohydride, formamidinesulphinic acid, glyceraldehyde, hydroxyacetone, hydroxylamine sulfate, lignin sulphonates, sodium formaldehydesulphoxylate, sodium hydrosulphite, thioglycolic acid, and various reducing sugars.
The prior art teaches the processing of only vat and sulfur dyes in a reducing medium. It has been believed that the use of direct dyes in such conditions would result in the destruction of the chromophore. Direct dyes may have been used to shade sulfur dyeings but not applied in combination with sulfur dyes dyed simultaneously in a reduction medium.
A process for dyeing a fibrous substrate which comprises the steps of: providing a fibrous substrate; providing at least one sulfur dye; providing at least one reduction stable direct dye; and applying said reduction stable direct dye and sulfur dye to said fibrous substrate in the presence of a suitable reducing agent.
Further, it has been surprising to find that these reduction stable direct dyes can be processed without a sulfur dye present. This results in a process for dyeing a fibrous substrate which comprises the steps of: providing a fibrous substrate; providing a reduction stable direct dye; and applying said reduction stable direct dye to said fibrous substrate in the presence of a suitable reducing agent.
Still further, it has been surprising to find that reduction stable direct dyes can be processed with vat dyes and optionally also sulfur dyes. The result is
a process for dyeing a fibrous substrate which comprises the steps of: providing a fibrous substrate; providing at least one vat dye; providing at least one reduction stable direct dye; and applying said reduction stable direct dye and vat dye to said fibrous substrate in the presence of a suitable reducing agent.